




THE COMMERCIAL ANALYSIS OF 

FURNACE GASES. 


The importance of making analyses of gases in furnaces which 
are used for metallurgical purposes is every day growing more and 
more evident. It is the only method of understanding the reactions 
that take place in the furnace, and of economically conducting the 
operations both with regard to the fuel used and the reactions which 
take place on the bodies to be subjected to the influence of the heat 
and gases. 

As a knowledge of the composition of gases is becoming every 
day more necessary to the proper conduct of furnace operations, it 
seems desirable that furnace managers should generally know that 
the analysis of gas for commercial purposes is neither difficult, 
tedious, or expensive, and that it does not necessarily imply the use 
of corrections requiring difficult instrumental observations and long 
and tedious mathematical calculations. 

Any method, therefore, which will tend to render these analyses 
simple will also tend to having them made and repeated as fre¬ 
quently as the analyses of the ores and other materials charged in 
the furnace. They should be made even more frequently, as their 
composition is affected by any change in the condition of the furnace, 
and a knowledge of their composition will give a ready clue to the 
unseen and otherwise not easily detected changes which are taking 
place. 

The only practicable method of making industrial analyses of gas 
is that of measuring volumes in graduated tubes. The methods by 
direct weight are too long and too complicated for commercial uses. 
The method by volumes has the double advantage that it can be 
made so exact in the hands of an expert as to be suitable for ultimate 
analyses, or it may be made so simple as to be within the capabili- 

1 



2 


THE COMMERCIAL ANALYSIS OF FURNACE GASES. 


ties of a common workman, who may be easily taught to determine 
volumes to within one-half per cent., which is a sufficiently close ap¬ 
proximation for any industrial purpose. 

It may be said in general terms that the normal working of any 

furnace will depend upon the ratio of and that it is in keep¬ 
ing the ratio of these two gases in proper relations that success¬ 
ful management depends. For ordinary commercial operations 
this relation can be determined in a few minutes, and is all the 
more important since it is desirable to know what it is, both at the 
entry of the gas into the furnace, and at its exit either into flues 
or into the air. By determining what this normal relation should 
be, it is quite possible to foresee the working of blast furnaces twenty- 
four hours ahead, and thus provide against accidents, and sometimes 
to bring down the consumption of fuel, and extend the length of a 
campaign very greatly* Accidents in blast furnaces will generally 
show themselves in their first stages in the composition of the gas at 
least twenty-four hours before they manifest themselves at the tuyeres 
or in the slag. An examination of the gas will, therefore, give a 
ready means of preventing them. 

It is not usually sufficient for this, however, to make single analy¬ 
ses at intervals; it is necessary that they should be repeatedly made, 
and that, as a general rule, the taking of the sample of the gas should 
be continued over several hours. 

While in some industrial gases the hydrocarbons, sulphurous 
acid, and occasionally chlorine are to be determined, for ordinary 
metallurgical purposes, the determination of carbonic acid, carbonic 
oxide, oxygen, and nitrogen (which will be the residue), only is nec¬ 
essary, since these are the gases which are principally affected by 
the process. As a general thing the hydrocarbons, except in gener¬ 
ators, are not found in any considerable quantity; nor is oxygen, 
except in furnaces where its presence is certain beforehand on account 
of its introduction in large quantities with air. To perform such an 
analysis in the works for commercial purposes the modified Orsat 
apparatus is the one which it is advisable to use. 

Since the description of the Orsat apparatus was published in Vol. 
II of the Transactions of the Institute , a large number of furnace 
managers have introduced it into their works, and are daily making 
use of it to control the working of their furnaces. The constant 
demand made for it in Europe and in this country has led to import¬ 
ant modifications ; and the importance of having a simple apparatus 
which can be put into the hands of workmen has brought about 


THE COMMERCIAL ANALYSIS OF FURNACE GASES. 


3 


several changes which tend to make it more portable and more 
complete. 

The Orsat apparatus as now modified does not differ in principle 
from that described in Vol. II of the Transactions. There has been 
added to it an appendage for the determination of hydrocarbons, 
which makes the apparatus more complete and useful in cases where 
mine gases are to be analyzed for the detection of fire-damp or for 
the examination of producer gases or any other gas. The shape of 
the apparatus, however, is somewhat different, the jars and bell 
glasses being replaced by U tubes. The volume of absorbent liquid 
used is also smaller, and the apparatus can consequently not be used 
so long without changing the liquid. This is, however, not a prac¬ 
tical difficulty, as the number of analyses, as was shown in Trans¬ 
actions, Vol. II, page 234, can be almost indefinite. 

This apparatus as now modified is shown in Fig. 1. It consists 
of a measuring-tube, A B, which is surrounded by water in order to 
have the gas at a constant temperature, and thus avoid the necessity 
of thermometers. The measuring-tube is open at both ends, and is 
fitted into the cooling tube by means of india-rubber corks. The 
bottom of the measurer is connected by means of a rubber tube 
with a small bottle, D, having an opening at the bottom, which con¬ 
tains acidulated water, and which is to serve both as an aspirator 
and expulsor of gas. The other end is connected with a small tube, 
which is not over a millimeter in diameter, which goes to the left of 
the measuring-tube. It has four arms, G, G', G", and I, each of 
which is provided with a glass stopcock. The prolongation of the 
tube itself is also provided with one at C. The one at the end 
connects with a tube, P, which is filled with cotton in order to filter 
smoke or dust from the gas which is drawn into the instrument 
through the rubber pipe, N. This filter connects by a glass tube at 
right angles, having a stopcock, R, with a trompe, L M, which is 
used both for aspiration and for clearing the apparatus of gas by con¬ 
necting it with a water-bottle by the tube, K. 

Each one of the U tubes is fitted to a wooden upright to which it 
is raised. The whole is then secured to the frame by thumbscrews, 
so that it can be easily removed to refill the tubes or alter the 
solutions. 

A German modification of the apparatus has the tubes with the 
stopcocks made of pewter. This is a very objectionable form of it, 
as it is much more likely to become foul. 

In order to be sure that the samples of gas taken for analyses 


4 


THE COMMERCIAL ANALYSIS OF FURNACE GASES. 


represent the mean composition of* the gases, they should be taken 
through a pipe with a long slot, and the gas collected should be 
passed through a Liebig condenser before it is used, so that it may 
be quite cool before it is introduced into the apparatus. The three 
stopcocks nearest the measurer connect with the U tubes, the first 


Fig. 1. 



one of which, ef, contains potash ; the second, e' f', pyrogallate of 
potash ; and the third, e" f", an ammoniacal solution of chloride of 
copper. The first is destined for the absorption of carbonic acid, the 
second for the absorption of oxygen, and the third for the carbonic 
oxide. These last gases may be determined together as described in 
Yol. II. When only the gases of a blast furnace are to be analyzed, 
two tubes are all that are necessary, but as the extra tube does not 
increase the difficulty of manipulation and the extra cost is very si ight, 
it is generally best to have three, as then the apparatus can be used 
in many cases where it would not be convenient to use two. 

A considerable difficulty has been found in the use of the ammo¬ 
niacal solution, it having been found to absorb very slowly. This 
solution, in order to have the greater surface, is formed by placing a 
roll of copper-wire gauze in the tubes. In order to get the requisite 
amount of surface it has been found desirable, with some gases, to 
replace this copper-wire by copper disks with short pieces of glass 











































































































































































THE COMMERCIAL ANALYSIS OF FURNACE GASES. 


5 


tubing between them. The slowness with which this solution works 
is caused, however, by the fact that the salt which produces the ab¬ 
sorption is not always present. The ammoniacal solution of chloride 
of copper absorbs oxygen very rapidly and forms an oxychloride 
of copper. When the oxychloride is formed the solution is blue, 
and when it is in this condition it absorbs the carbonic oxide rapidly ; 
but after a number of passages, the solution works very slowly and 
becomes green. In this case the oxychloride of copper, which is 
the absorbent, has been entirely used up, and it is necessary to make 
the solution blue again by the absorption of oxygen from the air, 
when it will absorb again as rapidly as at first. 

As the pyrogallate and oxychloride solutions are very sensitive, 
the ends of the U tubes, e'f and e"/", instead of being freely 
opened to the air are connected with rubber bags, the object of which 
is to prevent the access of the atmosphere. The oxygen of the air 
contained in the bags becomes rapidly absorbed, and the gas between 
the top of the solution and the interior of the bag in a short time 
will be composed of nothing but nitrogen. The details for using 
the left side of the apparatus are fully described in the article in 
Yol. II. In the complete apparatus, Fig. 2, the gallery is continued 
to the right, having a stopcock, J, on the gallery itself, and one pro¬ 
jecting tube, E, with a stopcock. The end of the gallery is attached 
to a spiral platinum tube, T (which is to be heated by an alcohol 
lamp, 01 by a Bunsen gas-burner placed below it), which connects 
with a stopcock, V, below it, by which the supply of gas is regulated. 
The apparatus is arranged for one or the other or both means of 
heating the platinum tube. There are connected with this gallery 
two U tubes, one of which, g' li ', serves as a reservoir, and the other, 
g li , is used for the production of hydrogen, which, with a large 
excess of air, is used to burn the hydrocarbons. There will be no 
danger, however, of an explosion, on account of the great excess of 
nitrogen and the capillarity of the tube. To insure complete com¬ 
bustion, the gas is mixed with a mixture of hydrogen and air. 

The gas having been passed through the left side of the apparatus, 
is transferred from the measurer to the capillary tube, and from 
there into the U tube, g f li' (partially filled with water), which serves 
as a reservoir for the gas. The other U tube, g h, which serves for 
the production of hydrogen, is cut off from the gallery by a stop¬ 
cock, E, while the transfer is made. It contains zinc and sulphuric 
acid, which, formed under pressure, throws the liquid back into the 
opposite side, thus forming a reservoir of hydrogen, and preventing 


6 


THE COMMERCIAL ANALYSIS OF FURNACE GASES 


the attack of the zinc except when it is necessary. In order to pre¬ 
vent the waste of zinc while the apparatus is not in use, the acid is 
cut off by the stopcock, X, which also serves to empty both tubes 
when it is necessary. 



When the hydrocarbons are to be determined, 200 divisions of 
the gas are taken, and all the gases that can be determined on the 
left side are separated first; 40 to 50 divisions are then taken for 
analysis, and all the remainder of the gas turned into the pyrogallate 




















































































































































































































































































































THE COMMERCIAL ANALYSIS OF FURNACE GASES. 


7 


solution,/' e'. Ten to fifteen divisions of hydrogen, and 130 to 150 
of ordinary air, taken through the tube, N, are then introduced, the 
quantities being determined by the supposed amount of hydrocar¬ 
bons present. The lamp, U, is lighted, and the mixture made to 
pass very slowly three or four times back and forth through the 
platinum spiral, T. Great care must be used not to introduce moist¬ 
ure into the platinum tube for fear of an explosion, which would 
break the glass tubes. The gas is then passed into the measurer, 
A B, and cooled, and the contraction read. In the burned gas car¬ 
bonic acid and oxygen are determined. If there is no oxygen the 
combustion has not been complete, as there has not been sufficient 
air, and fresh air and hydrogen may be added, or, better, the analysis 
may be commenced over again by using the reserve in the pyrogal- 
late tube. Complete combustion thus transforms the carbon into 
carbonic acid, and the hydrogen into water. 

The carbonic acid is determined directly by its absorption in the 
potash tube, ef. The amount of water produced must be calculated ; 
this is very easily done, for the quantity of air introduced is known, 
and if the number of divisions of it is represented by m, we have 
.021 m of oxygen, and .079 m of nitrogen; the nitrogen is unaffected 
and remains behind, while the .021 m of oxygen has been used to 
burn the hydrogen introduced into the U tube, and both the hydrogen 
and carbon of the hydrocarbon. Some of it has not been used, as 
the air must be in excess in order to be sure that the combustion 
has been complete. 

Of these four quantities, three are known. Oxygen in excess has 
been determined in the pyrogallate solution. The quantity of hy¬ 
drogen introduced is known. It has required for its combustion one- 
half its volume of oxygen. The carbon of the hydrocarbons has 
been transformed into carbonic oxide, to do which has required a 
volume of oxygen equal to its own. These volumes all being known, 
the quantity ot oxygen used to burn the hydrogen of the hydro¬ 
carbons is consequently known by difference. This quantity of 
oxygen has produced double its volume of water, and, consequently, 
all the elements for making the calculation of the hydrocarbons are 
known. 

The total volume of the hydrocarbons can also be determined, for 
after all the determinations have been made, the measuring-tube con¬ 
tains only nitrogen. This nitrogen is the sum of that contained in 
the gas and of that introduced with the air used to burn the carbon 
and hydrogen. The nitrogen contained in the gas was determined 


8 


THE COMMERCIAL ANALYSIS OF FURNACE GASES. 


before the gas passed the platinum spiral. The nitrogen in the air 
is known from the quantity of air introduced. Hence all the elements 
are determined. 

This method is sufficiently exact for all commercial purposes; the 
only inconvenience that it has is from the fact that as the oxygen to 
burn the carbon and hydrogen is all derived from the air, a quantity 
equal to fifteen times the total amount of the hydrocarbons to be 
analyzed must be introduced, besides which another amount must 
also be added sufficient to burn the hydrogen. This method is for 
commercial purposes much preferable, however, to using oxygen, as 
pure oxygen cannot always be had, and it would generally be im¬ 
practicable to have it on hand for industrial operations; besides which, 
the method is only a commercial one. Its errors, however, may be 
made to be not over one-half per cent. These errors are caused by the 
fact that the hydrocarbons are slightly soluble in the copper solution, 
and that acetylene, which some of these gases contain, precipitates the 
copper as an acetylide of copper. It is therefore not well adapted to 
complete analyses of hydrocarbons, or for the analysis of illuminating 
gas, but sufficiently exact to determine the presence of hydrogen and 
hydrocarbons in furnace gases or in fire-damp in mines, or for any 
ordinary commercial purpose. The very slight error is not sufficient 
to make any material change in determining the caloric powers of 
the different substances examined. 







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